Regular gas in a 9.5?

Why so reluctant ? It's not a farm vehicle !

Graham

Why still not even 90 octane ? The advice is *at least* 90 octane !

" Occasionally you get some genius who takes the opposite tack--he spends an extra 10 or 20 grand buying a high-performance car, then decides he's going to save three bucks per tankful using regular instead of premium as specified. He figures as long as the engine doesn't knock he's OK. Wrong, carbon monoxide brain. Car engines nowadays contain knock sensors that detect detonation and automatically retard the spark to compensate. The delay means maximum gas expansion occurs when the piston is farther along in its downstroke and thus there's more room in the cylinder head. This reduces peak cylinder pressure, eliminating knock but also giving you less power and poorer mileage. "

Graham

To resolve your problem, which is definitely not related to the grade of gasoline you are using, try swapping in some new spark plugs. Don't use anything except the proper NGK plain jane plugs called for in the owners manual.

From there on out, you should probably use 89 octane in a linear. There is no such thing as "90" octane in the US. It is 87 (regular), 89 (mid-grade) and 91 to 93 (super/premium) depending on location. The small difference between the gas certified to be 89 (or better) and 90 is pretty insignificant. If you wanted to be anal about it you could squirt in a few gallons of premium fuel every tankful of mid-grade, but since the mid grade is at least 89 (most likely somewhat more) it is not a very big deal.

OTOH, running the lowest grade as the PO did is not so great as it will cause the ECU to run with a retarded ignition timing pretty much all the time. You won't get the best mileage or best performance that way.

SPUTTER!

Thanks, Fred. What you say makes sense. I'll give the spark plug swap a go - couldn't hurt, surely - and continue with the 89 octane. FWIW, on this morning's 35 mile commute, I noticed none of the problems that I bitched about earlier.

Cheers,

M

I appreciate the 'straightdope,' Graham. I'm not trying to be cheap; I'm just trying to avoid the shedding of any shekels that I might otherwise have and hold, for better or for worse. What Fred said below, re: the 87 v. 89 v. 90 situation, seems to make sense to me. On the other hand, what I don't know about cars and engines is staggering, even to me. The Straightdope article was a help, and I need all of that that I can wrangle.

Cheers,

M

You're welcome.

By the way, do you work at Red Dot? Just curious based on your email addy. If so, I'm located just east of you a-ways in southern NH (Manchester area).

Yup. Red Dot, in Bondville, VT. Just shy of Manchester, VT.

M

Interesting, ain't it, our petrols over here are all unleaded and are

91, 96 and 98 octanes. My 9000 Aero likes 98 as recommended, but this is not available everywhere, so it usually runs happily on 96.

Cool Beans... and where, pray tell, is your domacile (35 miles away)? What a great gig that must be though, living large in the Green Mountains...

Ricky,

Your talking RON, and we rebel yanks are talking PON (Pump Octane Numbers) which is RON+MON/2. So your 96 is our 89. But I'm not entirely sure of the happiness of my SAAB's engine either way...

What is perhaps of interest (and maybe this was the point of you post) is that the bigger gap is between your "low grade" and your mid-grade. Why anyone would pay a big premium for 2 points of octane is a reasonable question. Here, the smaller gap which is between the low and mid grades (87 - 89) costs about 10 cents per gallon, and for another 10 centavos you get the big jump to 93 (4 points more)

In the UK many places only sell 95 RON ( e.g. supermarkets ) with an alternative 'superunleaded' being 97-98.

95 is fine for most cars but some perfromance vehicles get some extra performance from 97/98.

I'm puzzled by your suggestion that 96RON = 89PON. This table suggest more like

92PON. That also makes 95RON ( which I normally buy ) equal to 91PON which makes sense to me for use in a Saab.

Graham

Right you are... 96 RON should be about the same as 91 PON (aka AKI)

I'm not an expert, but a while back I remember that someone else had similar problems with a Saab at similar mileage, and I thought that it was a sign that the DI Casette was starting to fail? Can the repair-shop test this part to see if it's a problem, or is it a "I dunno, you could always replace it with a new one" kind of thing?

I bring this up, because when my casette went on my 9-3 at 84K or nearabouts, the car suddenly lost power while I was driving on a highway, and that was not a completely pleasant experience. And apparently, this is a known issue with Saab electronics (which Canada's "Lemon Aid" series of car guides has been slamming Saab for, for years).

Can an expert comment on this issue, to make sure we get the straight dope, please? Fred?

Thanks!

-- Viktor

Yes, I had considered the cassette as well. But when those fail they usually do, as yours did, suddenly and completely.

My experience has been that as the sparkplugs age you get intermittent problems such as what the OP has experienced. The plugs are cheap and can be put in by almost anyone (just don't over-torque them and strip ot the aluminum head). The change should be immediate and clear.

But the bottom line going back to the earlier post that some folks are missing the point of. You can use lower octane gas but you will get less power per gallon/liter and you will need to push on the pedal more for the same output. More gas per mile, less mpg.

As gas prices rise (at least in the USA) the actual per gallon difference between 87, 89, and 93 octane seems to remain the same. That means that on a percentage basis, the cost of using premium is on a steady decline. Since the percentage difference in mileage is not changing, the cost and advantage of using higher octane gas is increasing. Whether or not it makes sense to use premium for your driving style and conditions is something you need to test over multiple tank fills.

Fred-

You interest me strangely... when you say "almost anyone," do you really mean that? While I'm not a complete moron with things mechanical I'd have to admit to being somewhat more than a partial moron. Forgive this question in light of my last statement and tell me, doesn't the replacement of plugs require purpose-built and expensive tools and wrenches and things? If so, perhaps the purchase of said tool(s) would be offset by what I'd pay to have the things switched out. Yes? No?

Thanks,

M

It's 4 screws and one plug connector. It's the 4 button-head torx screws you can see on the top of the engine on the rectangular cover-looking thing covering the valley between the two cams, and the red connector on the right side as seen if you're standing where you have to be to be doing this.

Spark plug wrench, which is supplied with the car and should be under your trunk floor.

My 9000 2.0 LPT also runs better on Shell Optimax 97 or 98? Less likely to stall at full acceleration. These premium fuels also have cleaning agents which are beneficial.

No foolin'? That sounds eminently doable, if eminently is the word I want. But don't the tips of the plugs themselves need to calibrated one how or another (I've heard reference to "setting the gap") or are they factory set and good to go out of the box?

I appreciate this. Now I just have to figure out what a cam is.

Thanks,

Michael